The present invention relates generally to the field of magnetic data storage. In particular, the present invention relates to thermally stable high anisotropic FeCo(X, Y) films for writer pole materials.
In magnetic storage and retrieval systems, longitudinal storage media are approaching an upper limit of storage density. The discrete magnetized regions, or bits, which have magnetization vectors lying in the plane of the magnetic film, are approaching a size where they become thermally unstable. This is termed the superparamagnetic limit. In order to increase the storage density, systems have now been developed where the bits have magnetization vectors essentially normal to the film surface. These are called perpendicular storage and retrieval systems. The storage density of perpendicular systems can be an order of magnitude higher than longitudinal systems.
In perpendicular recording, the magnetic medium has the easy axis of magnetization perpendicular to the film surface. There is also a magnetically soft underlayer (SUL) between the recording layer and the substrate. A perpendicular read head includes a magnetically soft yoke, one or more turns of a conductor, a main pole and a return pole. The main pole is the write pole with submicron dimensions that defines the bit size. In contrast to longitudinal recording, where the bits are written with a fringing field, in perpendicular recording, the bits are generated with a deep gap field that passes through the magnetic layer into the SUL before it returns through the return pole.
Write poles of perpendicular transducers typically are of different materials than the rest of the yoke. Materials with high saturation magnetization, low coercivity and high magnetic anisotropy are desired. The rest of the yoke can be a soft magnetic material.
A consistent issue with perpendicular head recording is erase after write, (EAW) which is due to a delayed relaxation of the magnetization once the write current in the head is switched off. A remanent magnetization of the write pole causes erasure, which cannot be tolerated in a disc drive. High magnetic anisotropy in writer pole material that favors magnetization parallel to the disc surface will minimize or eliminate EAW. This same feature is desired in other magnetic head components such as shields and return poles.
Write pole materials must have high saturation magnetization, or moment, low coercivity and strong anisotropy. They must also have the thermal stability to withstand the temperature excursions during processing and afterwards. These properties are also required in magnetic shield components in longitudinal and perpendicular heads. One of the highest known moments at room temperature is exhibited by the alloy Fe65 Co35 which has a moment close to 2.4 T. FeCo films exhibiting magnetic anisotropy can be fabricated with off-axis static plasma deposition methods in which the plane of the substrate is tilted to the direction of the incident plasma. Unfortunately, anisotropic FeCo films deposited in this manner are not thermally stable and lose their anisotropy when subjected to elevated temperatures. There is a need, therefore, for magnetic film structures that have the moment, coercivity and anisotropy of FeCo that maintain anisotropy at elevated temperatures.